Question: Brandon is 3 times as old as Luis and is also 4 years older than Luis. How old is Brandon?
Explanation: We can use the given information to write down two equations that describe the ages of Brandon and Luis. Let Brandon's current age be $b$ and Luis's current age be $l$ $b = 3l$ $b = l + 4$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $b$ is to solve the second equation for $l$ and substitute that value into the first equation. Solving our second equation for $l$ , we get: $l = b - 4$ . Substituting this into our first equation, we get the equation: $b = 3$ $(b - 4)$ which combines the information about $b$ from both of our original equations. Simplifying the right side of this equation, we get: $b = 3b - 12$ Solving for $b$ , we get: $2 b = 12$ $b = 6$.